Recycling method for recycling calcium molybdate through cyclic alkaline leaching of waste molybdenum-nickel catalyst

Abstract

The invention belongs to the technical field of multi-metal resource wet recovery, and discloses a recovery method for recycling calcium molybdate from a waste molybdenum-nickel catalyst through cyclic alkaline leaching, which comprises the following steps: roasting molybdenum-nickel waste catalyst powder at 400-500 DEG C, cooling, grinding and crushing to obtain 80-120-mesh nickel-molybdenum waste catalyst powder, and recycling calcium molybdate from the nickel-molybdenum waste catalyst powder; and then primary alkaline leaching, neutralization impurity removal, neutralization value adjustment, molybdenum precipitation, cyclic alkaline leaching and calcium molybdate purification processes are performed once, and the obtained industrial-grade calcium molybdate can be sold after being washed and dried. According to the method, the waste molybdenum-nickel catalyst is adopted as the raw material, the calcium agent is adopted as the precipitator, alkali recycling and molybdenum recovery are achieved, the industrial-grade calcium molybdate product is obtained, the molybdenum product separation is achieved, meanwhile, acid addition for pH adjustment and impurity removal is not needed, and the method has the advantages of being low in agent cost, capable of saving alkali consumption, remarkable in economic benefit and the like.

Description

Technical Field

[0001] This invention relates to the field of recycling of polymetallic solid waste resources, and in particular to a method for recovering calcium molybdate by cyclic alkaline leaching of waste molybdenum-nickel catalyst. Technical Background Catalysts, through their key active components, can accelerate chemical reaction rates and improve production efficiency. They are widely used in hydrodesulfurization (HDS), hydronitrogenation (HDN), and hydroaromatics removal (HDA) processes in petroleum refining, automotive exhaust purification, and chemical metallurgy, accounting for over 90% of all applications. During use, catalysts can become poisoned due to impurities such as sulfur, phosphorus, and arsenic combining with active sites to form stable compounds, or due to carbonaceous deposits covering active sites or clogging pores, leading to catalyst failure. Catalysts typically require periodic replacement every 2-4 years. Catalysts removed during these periodic overhauls are considered spent catalysts. These spent catalysts become hazardous solid waste; direct landfilling would result in resource waste and environmental pollution. In particular, the high-value metals contained within them represent a vast "urban mine," making recycling and reuse highly valuable.

[0002] Therefore, recycling spent catalysts can not only improve local resource utilization and resource level, achieve energy conservation and carbon reduction, but also drive technological progress in my country's industry, promote the standardized integration of the secondary resource recycling industry of precious and non-ferrous metals and related industrial policy support, enhance the country's comprehensive strength, and achieve technological innovation, which is of great significance.

[0003] Traditional pyrometallurgy, which concentrates valuable metals through high-temperature smelting, has disadvantages such as extremely high energy consumption, severe equipment corrosion, and easy secondary pollution. It is gradually being replaced by hydrometallurgy and is only used for large-scale, rough recycling.

[0004] The main technical approach for waste agent recycling and resource utilization is a combination of pyrometallurgical and hydrometallurgical processes. After pretreatment in rotary kilns and roasting furnaces, the oil-containing organic substances are incinerated. The resulting residue containing valuable metals is then enriched through a smelting system to produce crude alloys for sale.

[0005] Chinese patent application number 202510645819.1 discloses a method for recovering valuable metals from vanadium-molybdenum-containing waste catalysts. The method involves roasting the vanadium-molybdenum-containing waste catalyst at 180–200°C, further heating to 450–500°C, and then cooling to obtain roasted material. The roasted material is then mixed with a sulfuric acid solution A containing oxalic acid and leached at 50–60°C to obtain leachate A and residue A. Residue A is then mixed with sulfuric acid containing thiourea and ethylenediaminetetraacetic acid. Solution B is mixed and heated to 70–80°C for a second leaching to obtain leachate B and residue B. Residue B is washed with acid and water to obtain a washing solution. The leachate and washing solution are combined to obtain a combined solution. S3: The pH of the combined solution is adjusted to 2.5–3, then adjusted to 4.5–5. Butanedione oxime alcohol solution is added, and the temperature is raised to 35–45°C to obtain a purified solution. The purified solution is then mixed evenly with the extract to obtain a vanadium-molybdenum-containing organic phase. S4: Back-extraction and product preparation. This method requires multiple heating and cooling cycles, and the wet reaction temperature varies, making temperature control complex.

[0006] Chinese patent application number 202011509206.9 discloses a method for recovering vanadium, molybdenum, nickel, and aluminum from spent catalysts in petroleum refining. This method involves vacuum pyrolysis of the spent catalyst to remove solid waste and heavy oil; followed by grinding; desulfurization and decarbonization of the resulting grinding residue followed by roasting to obtain roasted ore; sodium roasting of the roasted ore; and water leaching of the resulting sodium clinker to obtain a vanadium-molybdenum solution and nickel-aluminum slag. The vanadium-molybdenum solution undergoes sequential adsorption and desorption to obtain molybdic acid and waste liquid; and the nickel-aluminum slag is subjected to pressurized alkaline leaching to achieve the recovery of vanadium, molybdenum, nickel, and aluminum. This method requires vacuum pyrolysis of the spent catalyst, placing high demands on equipment; it requires multiple roasting processes, including desulfurization and decarbonization roasting, and high-temperature roasting to separate metals, resulting in high energy consumption; the molybdenum precipitation process requires adsorption and desorption, and the generated waste liquid and adsorbent materials can easily become new hazardous waste.

[0007] Chinese patent application number 202010731298.9 discloses a process for the wet recovery of iron, aluminum, nickel, molybdenum, and cobalt from spent hydrorefining catalysts. This process involves calcining and grinding the catalyst, followed by roughing using foam flotation. The roughed catalyst is then impregnated with dilute sulfuric acid, filtered, and the molybdenum-containing filter residue enters the next process. The filtrate undergoes stepwise precipitation to separate iron and aluminum. The filtered solution is then electrolyzed using anion exchange resin and an electrolytic cell. The cathode of the electrolytic cell recovers high-purity nickel and cobalt metals, while the anode recovers sulfuric acid solution under the action of the anion exchange resin. The molybdenum-containing filter residue is dissolved in the recovered sulfuric acid and electrolyzed; the cathode yields high-purity molybdenum metal, and the anode recovers sulfuric acid solution under the action of the anion exchange resin. This process requires voltage regulation, indicating the need for precise voltage control to balance efficiency and energy consumption. It is suitable for small- to medium-scale molybdenum and nickel recovery but not for large-scale production applications.

[0008] In existing technologies, the recovery of high-value metals from spent molybdenum-nickel catalysts mainly relies on hydrometallurgy. This process requires multiple adjustments to the pH value using acid / alkali, leading to high demands for acids and alkalis and increased waste such as salts, thus raising recovery costs. Therefore, a recovery technology and method that can reduce reagent dosage and lower metal recovery costs is needed. Summary of the Invention

[0009] The purpose of this invention is to provide a method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst. This method for recovering calcium molybdate by cyclic alkaline leaching mainly addresses the following problems: (1) The high-temperature sodium roasting technology for aluminum-based molybdenum-nickel waste catalysts has high energy consumption and high cost; (2) Using calcium hydroxide / calcium oxide instead of sodium hydroxide as an alkaline leaching agent significantly reduces costs, avoids the accumulation of sodium in the system, and reduces the amount of waste salt generated; and the use of circulating alkaline leaching and the use of raw materials to replace acidic neutralizing agents saves costs; (3) Maximize the concentration of valuable metals, increase the leaching kinetic rate of metals, and improve product purity.

[0010] The method of this invention, by utilizing the characteristics of raw materials and adjusting the pH during the reaction stage, can effectively reduce reagent consumption and achieve gradient purification and recycling of valuable metals. To achieve the above objectives, the following technical solution is adopted: According to one aspect of the present invention, the present invention provides a method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst, the recovery method comprising the following steps: (1) Catalyst calcination: The spent molybdenum-nickel catalyst powder is calcined at 400-500℃ for 1-2 hours, then cooled and ground to obtain 80-120 mesh spent nickel-molybdenum catalyst powder for later use; the purpose of low-temperature calcination is to convert the spent catalyst molybdenum sulfide into molybdenum trioxide and burn off all the organic oil in the spent catalyst to ensure that the organic matter and sulfides have no impact on the consumption of subsequent alkaline leaching agents and foam formation. (2) Initial alkaline leaching: The low-temperature roasted molybdenum-nickel waste catalyst powder is added to pure water to make a slurry, and initial alkaline solution and co-solvent are added. After heating and reacting for a period of time, solid-liquid separation is carried out to obtain initial alkaline leaching residue and initial alkaline leaching liquid. The initial alkaline leaching residue is then subjected to open-circuit separation of nickel-aluminum slag.

[0011] (3) Neutralization and impurity removal: Add waste catalyst powder to the alkaline leaching solution in step (2) for neutralization and impurity removal. After the neutralization reaction is completed, perform solid-liquid separation to obtain impurity removal residue and impurity removal solution. After washing and drying the impurity removal residue, aluminum hydroxide product is obtained, and the impurity removal solution enters the neutralization and value adjustment process. (4) Neutralization and adjustment: Add molybdenum-nickel waste catalyst powder to the impurity removal liquid in step (3) for neutralization and adjustment. After the reaction is completed, perform solid-liquid separation to obtain neutralization residue and neutralization liquid. Then return the neutralization residue to the initial alkaline leaching process in step (1) and enter the calcium oxide molybdenum precipitation process.

[0012] (5) Precipitation of molybdenum: Add lime milk to the neutralization solution in step (4) to precipitate molybdenum and the secondary molybdenum precipitation solution in step (7), filter to obtain coarse calcium molybdate precipitate and primary molybdenum precipitation solution, and the primary molybdenum precipitation solution enters the circulating alkaline leaching process. (6) Circulating alkaline leaching: Add molybdenum-nickel waste catalyst to the liquid after molybdenum precipitation, and add sodium hydroxide solution according to the final pH value, and heat to carry out circulating alkaline leaching. After the reaction is completed for a period of time, filter to obtain alkaline leaching residue and alkaline leaching liquid; the alkaline leaching residue is used for nickel-aluminum slag open circuit, and the alkaline leaching liquid is mixed with the impurity removal liquid obtained in step (3) and then enters the neutralization and adjustment process in step (4). This cycle is repeated. (7) Purification of calcium molybdate: After the crude calcium molybdate obtained in step (5) is slurried, it is added to the neutralized liquid obtained in step (4), reacted, filtered, and purified industrial-grade calcium molybdate and secondary molybdenum precipitation liquid are obtained; the secondary molybdenum precipitation liquid is returned to step (4), and the industrial-grade calcium molybdate is washed, dried and sold.

[0013] Preferably, in step (2), the initial alkaline solution is a sodium hydroxide solution with a mass concentration of 5% to 30%, the reaction time is 1 to 4 hours, the reaction temperature is 70 to 95°C, and the final pH value is 11.5 to 13.0. The purpose of the initial alkaline leaching is to leach out all aluminum and molybdenum, while retaining nickel in the alkaline leaching residue, thereby achieving nickel-aluminum open circuit, which is beneficial for the next step of forming aluminum products.

[0014] Preferably, in step (2), the co-solvent is a halide salt, which is one or a combination of sodium fluoride, sodium chloride, and potassium chloride. The proportion of the co-solvent added is 0.5% to 2.0% of the slurry mass. The co-solvent changes the ionic strength and coordination environment of the solution, which helps the oxidation reaction on the sulfide surface, allowing sulfur to be released from the crystal lattice, thereby accelerating the process of molybdenum entering the solution. It can also preferentially combine with impurity metal ions, purify the leachate, and protect the molybdenum recovery rate.

[0015] Preferably, in step (3), the pH value is adjusted to 8.0-8.5 by adding molybdenum-nickel waste catalyst powder, the impurity removal reaction time is 1-3 hours, and the impurity removal reaction temperature is 70-95℃; the sulfur-containing compounds in the molybdenum-nickel waste catalyst powder react with hydroxide ions to reduce the pH value of the solution, which is conducive to the precipitation of aluminum hydroxide in the solution to form aluminum hydroxide product.

[0016] Preferably, in step (4), the pH value is adjusted to 7.0-8.0 by adding spent molybdenum-nickel catalyst powder, the neutralization reaction time is 2-4 hours, and the reaction temperature is 70-95℃; adding a small amount of spent catalyst powder to adjust the pH value ensures the removal of impurities in the solution, which is beneficial to improving the purity of the subsequent calcium molybdate product.

[0017] Preferably, in step (5), the concentration of lime slurry added is 8% to 15%; the final pH value is 12.0 to 12.5; the reaction time is 10 min to 60 min; the reaction temperature is room temperature; the first calcium molybdate formed is crude calcium molybdate, and after multiple reactions and precipitation, the purity of the product is continuously improved, and finally the industrial grade calcium molybdate product is achieved.

[0018] Preferably, in step (6), the sodium hydroxide solution has a mass concentration of 5% to 30%, a reaction time of 1 to 4 hours, a reaction temperature of 70 to 95°C, and an endpoint pH of 11.5 to 13.0. The remaining solution after the calcium molybdate product purification is further improved to the same pH value as the initial alkaline leaching conditions and mixed with the spent molybdenum-nickel catalyst powder, and then enters the circulating alkaline leaching. The circulating alkaline leaching residue is mixed with the initial alkaline leaching residue and then enters the nickel-aluminum open circuit.

[0019] Preferably, the reaction time for calcium molybdate purification in step (7) is 1-2 hours, the reaction temperature is room temperature, and the final pH value is 10.5-11.0; ensuring that while calcium molybdate precipitates, other impurities remain in the residue.

[0020] Preferably, in step (2), the mass ratio of the molybdenum-nickel spent catalyst powder to water is 1:8-12. The technical solution adopted in this invention has the following significant effects: (1) This invention uses waste molybdenum-nickel catalyst as raw material and calcium agent as precipitant to realize the recycling of alkali and the recovery of molybdenum, and obtains industrial-grade calcium molybdate product. The recovery process of this invention can separate molybdenum product and increase the grade of calcium molybdate from 36% to 85% after cyclic alkali leaching. It does not require adding acid to adjust the pH to remove impurities. It has the advantages of low reagent cost, saving alkali consumption and significant economic benefits. Compared with high-temperature sodium roasting technology, energy consumption is significantly reduced.

[0021] (2) This invention uses waste catalyst powder to adjust pH, thus treating waste with waste, which greatly increases economic benefits and reduces reagent consumption costs by more than 40%. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for recovering calcium molybdate from waste molybdenum-nickel catalyst through cyclic alkaline leaching. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the present invention, and these aspects of the invention can be implemented even without these specific details.

[0024] Example 1 like Figure 1 As shown, the spent nickel-molybdenum catalyst is first roasted at 400℃ for 2 hours, resulting in a dry residue rate of 91.04%. The roasted residue is then ground to 80 mesh, with a molybdenum content of 5.35%, yielding nickel-molybdenum catalyst powder. This powder is then divided into multiple portions for sequential use. According to the present invention, a method for recovering calcium molybdate from spent nickel-molybdenum catalyst through cyclic alkaline leaching includes the following steps: (1) Initial alkaline leaching: Pure water and spent molybdenum-nickel catalyst powder were mixed at a liquid-solid ratio of 8:1 to form a slurry. An initial alkaline solution and a co-solvent were added. The co-solvent was sodium chloride, and the initial alkaline solution was a 5% sodium hydroxide solution. The amount of sodium chloride added was 0.5% of the volume (mass) of the slurry. The pH of the mixed slurry was adjusted to pH=11.01. The mixture was heated and reacted at 70℃ for 4 hours. Alkali was added continuously until the final pH=11.50. After solid-liquid separation, initial alkaline leaching residue and initial alkaline leaching solution were obtained. The initial alkaline leaching residue was fed into the nickel-aluminum open circuit. At this time, the dry residue rate was 90.4%, the molybdenum grade of the dry residue was 0.75%, and the molybdenum recovery rate was 87.33%.

[0025] (2) Neutralization and impurity removal: Molybdenum-nickel waste catalyst powder is added to the initial alkaline leaching solution after preliminary alkaline leaching to pH=8.0. After reacting at 70℃ for 3 hours, liquid-solid separation is carried out to obtain impurity-removed residue and impurity-removed solution. After washing and drying the impurity-removed residue, aluminum hydroxide product is obtained, and the impurity-removed solution enters the neutralization and adjustment process.

[0026] (3) Neutralization and pH adjustment: Add molybdenum-nickel spent catalyst powder to the purified liquid after neutralization and pH adjustment to 7.0. Neutralize at 70°C for 4 hours. After the reaction, separate the solid and liquid to obtain neutralization residue and neutralization liquid. Neutralization residue and molybdenum-nickel spent catalyst powder enter the initial alkaline leaching process together. In step (1) initial alkaline leaching process, the neutralization liquid enters the calcium oxide molybdenum precipitation process.

[0027] (4) Precipitation of molybdenum: After the neutralized liquid is mixed with the liquid after secondary molybdenum precipitation in the subsequent step (6), 8% lime milk is added to adjust the pH to 10. After reacting at room temperature for 60 minutes, the final pH is 12.0. Solid-liquid separation is performed to obtain crude calcium molybdate precipitate and liquid after primary molybdenum precipitation. The grade of crude calcium molybdate is 35.8%. The liquid after primary molybdenum precipitation enters the circulating alkaline leaching process.

[0028] (5) Circulating alkaline leaching: Molybdenum-nickel waste catalyst is added to the molybdenum precipitation liquid in proportion and mixed. 5% sodium hydroxide solution is added to adjust the pH to 11.04. The reaction is carried out at a temperature of 70℃. After 3 hours of reaction, the mixture is filtered. The final pH is 11.5. Solid-liquid separation is carried out by filtration to obtain circulating alkaline leaching residue and circulating alkaline leaching liquid. The circulating alkaline leaching residue enters the nickel-aluminum slag open circuit. The circulating alkaline leaching liquid is mixed with the impurity removal liquid and enters the neutralization and adjustment process. This cycle is repeated.

[0029] (6) Purification of calcium molybdate: The crude calcium molybdate obtained in step (4) is added to the slurry at a solid-liquid ratio of 5:1 and then added to the neutralized liquid obtained in the neutralization and adjustment process. At room temperature, 8% lime milk is added and the reaction is carried out for 2 hours. At the endpoint, the pH is 10.50. The mixture is filtered and separated to obtain purified industrial-grade calcium molybdate and the liquid after secondary molybdenum precipitation. The liquid after secondary molybdenum precipitation is returned to the neutralization and adjustment process. After multiple cycles, the industrial-grade calcium molybdate is washed, dried and sold. At this time, the grade of calcium molybdate is increased to 95.13%.

[0030] Example 2 like Figure 1 As shown, the spent nickel-molybdenum catalyst is first roasted at 450℃ for 1.5 hours, resulting in a dry residue rate of 91.04%. The roasted residue is then ground to 100 mesh, with a molybdenum content of 5.35%, yielding nickel-molybdenum catalyst powder. This powder is then divided into multiple portions for sequential use. According to the present invention, a method for recovering calcium molybdate from spent nickel-molybdenum catalyst through cyclic alkaline leaching includes the following steps: (1) Initial alkaline leaching: Pure water and spent molybdenum-nickel catalyst powder were mixed at a liquid-solid ratio of 10:1 to form a slurry. An initial alkaline solution and a co-solvent were added. The co-solvent was sodium chloride added at a ratio of 1% of the slurry volume (mass). The initial alkaline solution was a 25% sodium hydroxide solution. The pH of the mixed slurry was adjusted to pH=12.05. The mixture was heated and reacted at 85℃ for 3 hours. Alkali was added continuously until the final pH=12.20. After solid-liquid separation, initial alkaline leaching residue and initial alkaline leaching solution were obtained. The initial alkaline leaching residue was fed into the nickel-aluminum open circuit. At this time, the dry residue rate was 89.7%, the molybdenum grade of the dry residue was 0.74%, and the molybdenum recovery rate was 87.59%.

[0031] (2) Neutralization and impurity removal: Add molybdenum-nickel waste catalyst powder to the initial alkaline leaching solution after preliminary alkaline leaching until the pH reaches 8.34. After reacting at 85°C for 2 hours, liquid-solid separation is carried out to obtain impurity-removed residue and impurity-removed solution. After washing and drying the impurity-removed residue, aluminum hydroxide product is obtained, and the impurity-removed solution enters the neutralization and adjustment process.

[0032] (3) Neutralization and pH adjustment: Add molybdenum-nickel waste catalyst powder to the impurity removal liquid after neutralization and pH adjustment, adjust pH=7.32, and neutralize for 2 hours at 85℃. After the reaction, separate solid and liquid to obtain neutralization residue and neutralization liquid. Neutralization residue and molybdenum-nickel waste catalyst powder enter the initial alkaline leaching process together. In step (1) initial alkaline leaching process, the neutralization liquid enters the calcium oxide molybdenum precipitation process.

[0033] (4) Precipitation of molybdenum: After neutralizing and adjusting the pH value, the neutralized solution is mixed with the secondary molybdenum precipitation solution in the subsequent step (6), and 10% lime milk is added to adjust the pH value to 10.04. After reacting at room temperature for 45 minutes, the final pH value is 12.2. Solid-liquid separation is performed to obtain crude calcium molybdate precipitate and primary molybdenum precipitation solution. The grade of crude calcium molybdate is 36.5%. The primary molybdenum precipitation solution enters the circulating alkaline leaching process. (5) Circulating alkaline leaching: Molybdenum-nickel waste catalyst is added to the molybdenum precipitation liquid in proportion and mixed. Sodium hydroxide solution with a concentration of 25% is added to adjust the pH to 11.79. The reaction is carried out at a temperature of 85℃ for circulating alkaline leaching. After 2 hours of reaction, the mixture is filtered. The final pH is 12.10. Solid-liquid separation is carried out by filtration to obtain circulating alkaline leaching residue and circulating alkaline leaching liquid. The circulating alkaline leaching residue enters the nickel-aluminum slag open circuit. The circulating alkaline leaching liquid is mixed with the impurity removal liquid and enters the neutralization and adjustment process. This cycle is repeated.

[0034] (6) Purification of calcium molybdate: The crude calcium molybdate obtained in step (4) molybdenum precipitation process is added to the slurry at a solid-liquid ratio of 5:1, and then added to the neutralized liquid obtained in the neutralization and adjustment process. At room temperature, 10% lime milk is added, and the reaction is carried out for 1.5 hours. At the endpoint, the pH is 10.80. The mixture is filtered and separated to obtain purified industrial-grade calcium molybdate and the liquid after secondary molybdenum precipitation. The liquid after secondary molybdenum precipitation is returned to the neutralization and adjustment process. After multiple cycles, the industrial-grade calcium molybdate is washed, dried, and sold. At this time, the grade of calcium molybdate is increased to 95.67%.

[0035] Example 3 like Figure 1 As shown, the spent nickel-molybdenum catalyst is first roasted at 500℃ for 1 hour, resulting in a dry residue rate of 91.04%. The roasted residue is then ground to 120 mesh, with a molybdenum content of 5.35%, yielding nickel-molybdenum catalyst powder. This powder is then divided into multiple portions for sequential use. According to the present invention, a method for recovering calcium molybdate from spent nickel-molybdenum catalyst through cyclic alkaline leaching includes the following steps: (1) Initial alkaline leaching: Pure water and spent molybdenum-nickel catalyst powder were mixed at a liquid-to-solid ratio of 12:1 to form a slurry. An initial alkaline solution and a co-solvent were added. The co-solvent was potassium chloride added at a ratio of 2% by volume (mass) of the slurry. The initial alkaline solution was a 30% sodium hydroxide solution. The pH of the mixed slurry was adjusted to pH=12.04. The mixture was heated and reacted at 95℃ for 1 hour. Alkali was added continuously until the final pH=13.0. After solid-liquid separation, initial alkaline leaching residue and initial alkaline leaching solution were obtained. The initial alkaline leaching residue was fed into the nickel-aluminum open circuit. At this time, the dry residue rate was 90.9%, the molybdenum grade of the dry residue was 0.69%, and the molybdenum recovery rate was 88.28%.

[0036] (2) Neutralization and impurity removal: Add molybdenum-nickel waste catalyst powder to the initial alkaline leaching solution after preliminary alkaline leaching until the pH reaches 8.50. After reacting at 95°C for 1 hour, liquid-solid separation is performed to obtain impurity-removed residue and impurity-removed solution. After washing and drying the impurity-removed residue, aluminum hydroxide product is obtained, and the impurity-removed solution enters the neutralization and adjustment process.

[0037] (3) Neutralization and pH adjustment: Add molybdenum-nickel spent catalyst powder to the purified liquid after neutralization and pH adjustment to 8.0. Neutralize at 70°C for 4 hours. After the reaction, separate the solid and liquid to obtain neutralization residue and neutralization liquid. The neutralization residue and molybdenum-nickel spent catalyst powder enter the initial alkaline leaching process together. In step (1) initial alkaline leaching process, the neutralization liquid enters the calcium oxide molybdenum precipitation process.

[0038] (4) Precipitation of molybdenum: After neutralizing and adjusting the pH value, the neutralized liquid is mixed with the liquid after secondary molybdenum precipitation in step 2 (6), and 15% lime milk is added to adjust the pH value to 10.05. After reacting at room temperature for 10 minutes, the final pH value is 12.50. Solid-liquid separation is performed to obtain crude calcium molybdate precipitate and liquid after primary molybdenum precipitation. The grade of crude calcium molybdate is 37.4%. The liquid after primary molybdenum precipitation enters the circulating alkaline leaching process.

[0039] (5) Circulating alkaline leaching: Molybdenum-nickel waste catalyst is added to the molybdenum precipitation liquid in proportion and mixed. 30% sodium hydroxide solution is added to adjust the pH to 12.15. The reaction is carried out at a temperature of 95℃ for circulating alkaline leaching. After 1 hour of reaction, the mixture is filtered. The final pH is 13.00. Solid-liquid separation is carried out by filtration to obtain circulating alkaline leaching residue and circulating alkaline leaching liquid. The circulating alkaline leaching residue is fed into the nickel-aluminum slag open circuit. The circulating alkaline leaching liquid is mixed with the impurity removal liquid and enters the neutralization and adjustment process. This cycle is repeated. (6) Purification of calcium molybdate: The crude calcium molybdate obtained in step (4) molybdenum precipitation process is added to the slurry at a solid-liquid ratio of 5:1, and then added to the neutralized liquid obtained in the neutralization and adjustment process. At room temperature, 15% lime milk is added, and the reaction is carried out for 1 hour. At the endpoint, the pH is 11.00. The mixture is filtered and separated to obtain purified industrial-grade calcium molybdate and the liquid after secondary molybdenum precipitation. The liquid after secondary molybdenum precipitation is returned to the neutralization and adjustment process. After multiple cycles, the industrial-grade calcium molybdate is washed, dried, and sold. At this time, the grade of calcium molybdate is increased to 95.21%.

[0040] Example 4 (Comparative Example of High-Temperature Sodium Roasting) High-temperature sodium roasting follows the existing high-temperature sodium roasting process: raw material molybdenum grade 5.35%, roasting temperature 900℃, roasting time 1 hour, alkali-to-molybdenum ratio (molar ratio of sodium carbonate to molybdenum oxide) 2.0. After the reaction, pure water is added at a liquid-to-solid ratio of 3:1, the mixture is slurried, filtered, the filter residue is washed, dried, and weighed. The dry residue rate is 85.6%, the residue contains 0.66% molybdenum, and the molybdenum recovery rate is 89.44%. Calcium chloride is added to the water leaching solution to precipitate molybdenum. After solid-liquid separation, the calcium molybdate is washed and dried, at which point the calcium molybdate grade is 49.6%.

[0041] Example 5 (Comparative Example of Alkali Leaching under Normal Pressure) Atmospheric pressure alkaline leaching process: The raw material molybdenum grade is 5.35%, and pure water is added at a liquid-to-solid ratio of 10:1 to make a slurry. Sodium hydroxide is used to adjust the pH to 12.5, and the reaction is carried out for 1 hour. After the reaction is completed, the slurry is filtered, the filter residue is washed, dried, and weighed. The dry residue rate is 91.2%, the residue contains 0.80% molybdenum, and the molybdenum recovery rate is 86.36%. Calcium chloride is added to the water leaching solution to precipitate molybdenum. After solid-liquid separation, the calcium molybdate is washed and dried. At this time, the calcium molybdate grade is 47.4%.

[0042] The principle and steps of this invention are as follows: (1) Low-temperature roasting After being pulverized, the spent molybdenum-nickel catalyst is subjected to low-temperature roasting at 400–500°C, where molybdenum sulfide is converted to molybdenum trioxide. Nickel sulfides, however, are relatively stable and require temperatures above 600°C to disrupt their crystal structure, thus preserving nickel sulfide from conversion. The low-temperature roasting reaction equation is as follows: 2MoS2 + 7O2 → 2MoO3 + 4SO2↑ In the existing high-temperature sodium calcination process, molybdenum sulfide undergoes a sodium calcination reaction with sodium carbonate, and the reaction equation is as follows: 2MoS2+6Na2CO3+9O2→2Na2MoO4+4Na2SO4+6CO2↑; Al2O3+ Na2CO3→ 2NaAlO2+ CO2↑; 3MoO3 + Al2O3 → Al2(MoO4)3; Therefore, in the existing high-temperature sodium roasting process, a large amount of aluminum forms aluminate ions which enter the subsequent water leaching solution, affecting the molybdenum recovery rate. Simultaneously, the formed aluminum molybdate is poorly soluble in water, preventing molybdenum from transferring to the aqueous phase during water leaching, resulting in a high molybdenum content in the leaching residue and further impacting molybdenum recovery. In contrast, the low-temperature roasting technology achieves complete combustion of oil-containing substances while selectively converting molybdenum sulfide into molybdenum oxide, without converting nickel sulfide. This avoids the formation of aluminum molybdate, reducing energy consumption and costs.

[0043] (2) Initial alkaline leaching The molybdenum-nickel waste catalyst powder after low-temperature roasting was added to the pulping water at a certain liquid-solid ratio, and alkali was added in proportion to adjust the pH value. After the reaction was completed, the mixture was filtered. MoO3 + 2NaOH → Na2MoO4 + H2O (main reaction); Al2O3 + 2NaOH → 2NaAlO2 + H2O (side reaction); During the alkaline leaching process, some aluminum is dissolved into sodium aluminate and enters the solution. However, since the reaction temperature is much lower than the sodium roasting temperature, the aluminum concentration entering the alkaline leaching solution is low, which reduces the impact on molybdenum recovery. The molybdenum content of the primary alkaline leaching residue is about 0.5% to 0.8%.

[0044] (3) Neutralization and impurity removal, neutralization and value adjustment. Aluminum hydroxide acts as a base in an acidic environment (pH < 4), reacting with acids to produce soluble aluminum salts; while in an alkaline environment (pH > 10), it acts as an acid, reacting with bases to generate soluble tetrahydroxyaluminate ions; and within a pH range of 7-8, aluminum hydroxide is sufficiently precipitated. Adding spent molybdenum-nickel catalyst powder to the initial alkaline leaching solution lowers the pH, which facilitates the removal of impurities from the solution and improves the purity of molybdenum.

[0045] (4) Molybdenum precipitation Sodium molybdate in the neutralization solution undergoes a metathesis reaction with calcium oxide to produce sodium hydroxide and calcium molybdate, which is sparingly soluble in water. During this reaction, if the pH is too low, the molybdate ion readily hydrolyzes to produce metamolybdate.

[0046] Na2MoO4+ CaO + H2O → CaMoO4↓ + 2NaOH (5) Circulating alkaline leaching and calcium molybdate purification Reprecipitating molybdenum in the alkaline leaching solution after removing impurities not only facilitates the recovery of molybdenum from the solution but also reduces the impurity content in the system. Furthermore, through continuous circulation, the grade of the target product, calcium molybdate, can be improved.

[0047] The method for recovering calcium molybdate from waste molybdenum-nickel catalyst by cyclic alkaline leaching of the present invention has the following advantages compared with methods such as high-temperature sodium roasting and room-temperature alkaline leaching (experimental results are shown below): 1. The comparative experiment of calcium molybdate products is shown in Table 1: Table 1: Product Comparison Experiment Results Data Compared with existing processes, the technical solution of this invention effectively improves the grade of calcium molybdate through multiple cycles of alkaline leaching, thereby increasing the product value.

[0048] 2. A comparison of energy consumption costs is shown in Table 2: Table 2: Energy Consumption Comparison Data Based on an annual processing capacity of 10,000 tons, this invention will increase economic benefits by approximately 900,000 yuan per year.

[0049] 3. Reagent costs are shown in Table 3. Table 3: Comparison of Reagent Costs Compared with the atmospheric pressure alkaline leaching method, the reagent cost is significantly reduced. Based on an annual processing scale of 10,000 tons, the present invention will increase the economic benefits by approximately RMB 1.4118 million per year.

[0050] In summary, the present invention provides a method for recovering calcium molybdate by cyclic alkaline leaching of waste molybdenum-nickel catalyst, which has significant economic benefits, greatly increases economic efficiency, reduces reagent consumption costs, and improves the grade of calcium molybdate.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst, characterized in that, The recycling method includes the following steps: (1) Catalyst calcination: The spent molybdenum-nickel catalyst powder is calcined at 400-500℃ for 1-2 hours, then cooled and ground to obtain 80-120 mesh spent nickel-molybdenum catalyst powder for later use. (2) Initial alkaline leaching: The low-temperature roasted molybdenum-nickel waste catalyst powder is added to pure water to make a slurry, and initial alkaline solution and co-solvent are added. After heating and reacting for a period of time, solid-liquid separation is carried out to obtain initial alkaline leaching residue and initial alkaline leaching solution. The initial alkaline leaching residue is then subjected to open-circuit separation of nickel-aluminum slag. (3) Neutralization and impurity removal: Add waste catalyst powder to the alkaline leaching solution in step (2) for neutralization and impurity removal. After the neutralization reaction is completed, perform solid-liquid separation to obtain impurity removal residue and impurity removal solution. After washing and drying the impurity removal residue, aluminum hydroxide product is obtained, and the impurity removal solution enters the neutralization and value adjustment process. (4) Neutralization and adjustment: Add molybdenum-nickel waste catalyst powder to the impurity removal liquid in step (3) for neutralization and adjustment. After the reaction is completed, perform solid-liquid separation to obtain neutralization residue and neutralization liquid. Then return the neutralization residue to the initial alkaline leaching process in step (1) and put the neutralization liquid into the calcium oxide molybdenum precipitation process. (5) Precipitation of molybdenum: Add lime milk to the neutralization solution in step (4) to precipitate molybdenum and the secondary molybdenum precipitation solution in step (7), filter to obtain coarse calcium molybdate precipitate and primary molybdenum precipitation solution, and the primary molybdenum precipitation solution enters the circulating alkaline leaching process. (6) Circulating alkaline leaching: Add molybdenum-nickel waste catalyst to the liquid after molybdenum precipitation, and add sodium hydroxide solution according to the final pH value, and heat to carry out circulating alkaline leaching. After the reaction is completed for a period of time, filter to obtain alkaline leaching residue and alkaline leaching liquid; the alkaline leaching residue is used for nickel-aluminum slag open circuit, and the alkaline leaching liquid is mixed with the impurity removal liquid obtained in step (3) and then enters the neutralization and adjustment process in step (4). This cycle is repeated. (7) Purification of calcium molybdate: After the crude calcium molybdate obtained in step (5) is slurried, it is added to the neutralized liquid obtained in step (4), reacted, filtered, and purified industrial-grade calcium molybdate and secondary molybdenum precipitation liquid are obtained; the secondary molybdenum precipitation liquid is returned to step (4).

2. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (2), the initial alkaline solution is a sodium hydroxide solution with a mass concentration of 5% to 30%, the reaction time is 1 to 4 hours, the reaction temperature is 70 to 95°C, and the final pH value is 11.5 to 13.

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3. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (2), the co-solvent is a halide salt, which is one or a combination of sodium fluoride, sodium chloride, and potassium chloride. The proportion of the co-solvent added is 0.5% to 2.0% of the mass of the slurry.

4. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (3), the pH value is adjusted to 8.0-8.5 by adding molybdenum-nickel waste catalyst powder, the impurity removal reaction time is 1-3 hours, and the impurity removal reaction temperature is 70-95℃.

5. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (4), the pH value is adjusted to 7.0-8.0 by adding molybdenum-nickel waste catalyst powder, the neutralization reaction time is 2-4 hours, and the reaction temperature is 70-95℃.

6. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (5), the concentration of lime slurry added is 8% to 15%; the final pH value is 12.0 to 12.5; the reaction time is 10 min to 60 min; and the reaction temperature is room temperature.

7. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (6), the sodium hydroxide solution has a mass concentration of 5% to 30%, the reaction time is 1 to 4 hours, the reaction temperature is 70 to 95°C, and the final pH value is 11.5 to 13.

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8. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: The reaction time for calcium molybdate purification in step (7) is 1-2 hours, the reaction temperature is room temperature, and the final pH value is 10.5-11.

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9. The method for recovering calcium molybdate by cyclic alkaline leaching of spent molybdenum-nickel catalyst according to claim 1, characterized in that: In step (2), the mass ratio of the molybdenum-nickel waste catalyst powder to water is 1:8-12.

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